For prevention of air pollution, wet-type limestone-gypsum desulfurizers have been widely put into practical use as apparatuses that remove sulfur oxide and the like contained in exhaust gases. This wet-type exhaust gas desulfurizer has such a structure, as shown in FIG. 11, that an exhaust gas emitted from a combustion apparatus such as a boiler is introduced into an absorption tower 1 through an inlet flue 2, and as a result of contact with droplets of an absorption liquid of a slurry including limestone or lime or the like sprayed from spray nozzles 5 respectively provided on spray headers 3 installed in the absorption tower 1 and provided in multiple stages along the direction of an exhaust gas flow, SOx in the exhaust gas is absorbed along with acid gases such as hydrogen chloride (HCl), hydrogen fluoride (HF), and the like in the exhaust gas. Simultaneously, soot and dust caused by components contained in the fuel used by the combustion apparatus and other substances are absorbed and removed by the absorption liquid.
Moreover, mist made to accompany the exhaust gas is removed by a mist eliminator 7 installed in an outlet flue 4 of the absorption tower 1, and a clean exhaust gas passes through the outlet flue 4, is reheated as necessary and emitted from a funnel. An SOx absorbent, for example, limestone, is fed as a limestone slurry 8 into a liquid trapping section 9 of the absorption tower 1 by an unillustrated limestone slurry pump according to the amount of SOx absorption.
The absorption liquid in the liquid trapping section 9 is extracted by a plurality of absorption liquid circulation pipes 11 that connect with the liquid trapping section 9, raised in pressure by absorption tower circulation pumps 12 provided on the circulation pipes 11, sent to the spray headers 3 connected to the respective circulation pipes 11, respectively, and then sprayed from the spray nozzles 5. The exhaust gas that rises inside the absorption tower 1 makes gas-liquid contact with the sprayed absorption liquid droplets, and SOx and the like in the exhaust gas are absorbed and removed.
The SOx in the exhaust gas reacts with calcium in the absorption liquid to form calcium sulfite (including calcium bisulfite) as an intermediate product, falls in the liquid trapping section 9, and is oxidized into gypsum by air 14 fed to the liquid trapping section 9 while being raised in pressure by an unillustrated air blower or the like to be an end product (gypsum). By thus directly feeding air into the absorption tower 1, an absorption reaction of SOx in the exhaust gas and an oxidation reaction of the produced calcium sulfite are made to progress simultaneously, whereby a desulfurization reaction as a whole can be promoted.
Also, the air 14 to be fed to the liquid trapping section 9 at that time is miniaturized by an oxidizing agitator 15 to thereby increase the utilization rate of oxidization air. Thereafter, the absorption liquid slurry is extracted from the liquid trapping section 9 while being raised in pressure by an extraction pump 16 according to the amount of produced gypsum, sent to gypsum dehydration equipment 17, and collected as powder gypsum.
In recent years, there have been an increasing number of cases where a large capacity of exhaust gas from a large-capacity boiler or a plurality of boilers is treated by one absorption tower 1 for improvement in reliability of a wet-type exhaust gas desulfurizer and from an economic perspective. Moreover, when the concentration of SOx in an exhaust gas is high or when highly efficient desulfurization of a large capacity of exhaust gas or an exhaust gas with a high SOx concentration is required, the necessary desulfurization performance is satisfied by increasing the amount of circulation spray of the absorption tower 1.
Particularly in a plant where highly efficient desulfurization of a large capacity of exhaust gas with a high SOx concentration is required, the amount of liquid circulated through the absorption tower is increased. On the other hand, due to restriction on the capacity of absorption liquid to be sprayed by the spray nozzles 5 attached to the absorption tower spray header 3 and the installing number of spray nozzles 5 to be attached to each absorption tower spray header 3 and restriction on liquid feeding amount performance of the circulation pump 12, there is restriction on the amount of absorption liquid to be circulatively fed to the spray nozzles 5, and thus multiple stages of spray headers 3 are installed.
In the above conventional art, the spray nozzles 5 installed in an absorbing section of the absorption tower 1 are arranged in a grid form so as to have as equal intervals as possible. Also, here, hollow cone-type spray nozzles 5 having spray angles of, as shown in FIG. 9, approximately 90 degrees with respect to a direction orthogonal to an exhaust gas flow are mainly used.
Patent Document 1: Japanese Published Unexamined Patent Application No. 2004-24945
Patent Document 2: Japanese Published Unexamined Patent Application No. H11-179144